Abstracts of slected journal articles

The historical development of packet switching technology in the late sixties and the events which led to the implementation of the first packet switched military co=~unications system, ARPANET, are outlined. The development of the US data networks TYMNET and TELENET in the early seventies and other North American networks, DATAPAC and INFOSWITCH in Canada and SCT in Mexico, is reviewed. The status of national and international packet switched networks in Western Europe and Southeast Asia is also examined and the following networks are described: The linking of networks within and between the three major networking sites in North America, Western Europe and Southeast Asia and the impact of packet switching technology on online information retrieval are briefly discussed. This article provides a broad overview of the development of abstracting and indexing services in science and technology during the last three and one-half decades. It identifies major trends that have clearly affected individual producers, services, and the field as a whole. These trends include the changing national priorities, the new technologies, and the growing importance of marketing. Change, transformation, and survival are keywords in the discussion. The Maximum Entropy Principle is a body of statistical theory addressed to the problem of how to make probability estimates in the fact of an apparent